Concentration dependent phase transition of a small protein in synthetic lipid multilayers

Author

Ludtke, Steven J.

Date

1993

Degree

Master of Arts

Abstract

We present evidence that magainin I, a 23 residue antibiotic peptide, undergoes a concentration dependent phase transition in synthetic lipid multilayers. Using oriented circular dichroism (OCD) we show that in low concentrations, magainin forms $\alpha$-helices lying parallel to the membrane surface. When the concentration becomes greater than a lipid specific value, the magainin undergoes a conformational change to a yet unidentified state. The state of the system at concentrations above the critical concentration shows that this transition cannot be explained by the micellar effect. Correlations between our results and liposome leakage experiments indicate that this transition is responsible for magainin's antibiotic action.